This invention relates to a valve-moving apparatus for an internal combustion engine for controlling operation of an intake valve and an exhaust valve disposed in an automobile engine and the like.
In general, in open/close control of an intake valve and an exhaust valve of an automobile engine, the open/close timing is set according to the operating condition obtained from an engine rotation speed, the amount of depression of an accelerator pedal, and the like. In such a valve-moving apparatus, there is proposed one which varies a cam profile according to the operation condition to improve the fuel consumption at a low speed and improve volumetric efficiency into the cylinders at a high speed. This is achieved by varying the open/close timing, lift amount, release time, and the like of the intake and exhaust valves at a low or a high speed.
Specifically, the automobile engine is provided with a high-speed cam and a low-speed cam, the high-speed cam having a cam profile which is able to obtain a valve open/close timing for high-speed operation, and on the other hand, the low-speed cam has a cam profile which is able to obtain a valve open/close timing for low-speed operation. During operation of the engine, the high-speed cam or the low-speed cam can be selectively used according to the operating condition to obtain an optimum open/close timing of the intake and exhaust valves.
Further, in such an automobile engine, there has previously been proposed a cylinder-closing mechanism which stops operation of two of four cylinders of a 4-cylinder engine to improve the gas mileage. That is, in the valve-moving apparatus, during idle operation or low-load operation, the piston operates but operation of the intake and exhaust valves is stopped to discontinue supply of fuel. This cylinder-closing mechanism for stopping operation of the intake and exhaust valves is generally operated by providing a change-over mechanism in the rocker arm and hydraulically controlling the change-over mechanism. In this case, hydraulic pressure is supplied from a main oil pump of the engine to the change-over mechanism through an oil passage.
Such a valve-moving apparatus having a cylinder-closing mechanism has already been applied for a patent by the Applicant of the present application as JP Patent Application No. 4-43030 Feb. 28, 1993). FIG. 14 shows a plan view of a valve-moving apparatus having a prior art cylinder-closing mechanism of the prior application by the Applicant, and FIG. 15 shows an XV--XV cross sectional view of FIG. 14.
In an engine having a cylinder-closing mechanism, for a 4-cylinder engine, for example, two cylinders thereof have valve-moving apparatus with cylinder-closing mechanisms, and the remaining two cylinders have valve-moving apparatus with no cylinder-closing mechanisms. As shown in FIG. 14 and FIG. 15, in a cylinder head (not shown), a pair of cam shafts 203 are integrally formed with a low-speed cam 201 and high-speed cam 202. Similarly, a pair of rocker shaft parts 204 are rotatably supported parallel to the cam shafts 203. A base of arm parts 205 is integrally mounted to the rocker shaft parts 204, and the bases of a low-speed rocker arm 206 and a high-speed rocker arm 207 are individually rotatably mounted to the rocker shaft parts 204. A rocking end of the arm parts 205 opposes each of the top ends of an intake valve 301 and an exhaust valve 302. And roller bearings 208 and 209 engaging with the low-speed cam 201 and the high-speed cam 202 are respectively mounted to the rocking ends of the low-speed rocker arm 206 and the high-speed rocker arm 207.
In the rocker shaft parts 204, a low-speed rock pin 210 and a high-speed rock pin 211 are movably supported along axial directions at positions corresponding to the low-speed rocker arm 206 and the high-speed rocker arm 207, respectively. The low-speed rock pin 210 is urged in a direction to engage with the low-speed rocker arm 206, and the high-speed rock pin is urged in a direction releasing from the high-speed rocker arm 207. The rocker shaft parts 204 are formed with a low-speed side hydraulic pressure passage and a high-speed side hydraulic pressure passage (not shown), and the low-speed side and high-speed side hydraulic pressure passages are connected with hydraulic pressure control means for setting hydraulic pressure and controlling operation of the individual rock pins 210 and 211.
Further, on the low-speed rocker arm 206 and the high-speed rocker arm 207, projection parts 212 and 213 are integrally formed individually at the opposite sides to the rocking ends to which the roller bearings 208 and 209 are mounted, with the projection parts 212 and 213 being urged by the arm springs 214 and 215. The arm springs 214 and 215 are formed by a structure in which a plunger 217 movably engages with a cylinder 216 fixed to the cylinder head side and a compression spring 218 is disposed, a free end of the plunger 217 pressing the projection parts 212 and 213 to urge individually the low-speed rocker arm 206 clockwise and the high-speed rocker arm 207 counter-clockwise
Therefore, usually, for the low-speed rocker arm 206 and the high-speed rocker arm 207, the roller bearings 208 and 209 contact against the outer peripheral surfaces of the low-speed cam 201 and the high-speed cam 202 due to the biasing forces of the arm springs 214 and 215, so that the individual rocker arms 206 and 207 will not freely rotate even when the low-speed rock pin 210 does not engage with the low-speed rocker arm 206 and the high-speed rock pin does not engage with the high-speed rocker arm 207.
When the engine is in a low-speed traveling condition, the low-speed rocker arm 206 and the rocker shaft parts 204 become integral due to the rock pin 210. When the cam shaft 203 rotates, the low-speed rocker arm 206 is rocked by the low-speed cam 201; the driving force is transmitted to the arm parts 205 through the rocker shaft parts 204 to rock the arm parts, and the rocking end drives the intake valve 301 and the exhaust valve 302. Thus, the engine is operated at a low speed.
When the engine is in a high-speed traveling condition, the rock pin 210 is released to disengage the low-speed rocker arm 206, while the rock pin 211 is engaged with the high-speed rocker arm 207. Therefore, the high-speed rocker arm 207 is rocked by the high-speed cam 202, the arm parts 205 rock to drive the individual valves 301 and 302, and the engine is operated at a high speed.
When the engine is in an idling or low-load traveling condition, the rock pin 210 is disengaged to release the low-speed rocker arm 206, the driving force of the low-speed cam 201 and the high-speed cam 202 is not transmitted to the arm parts 205, and this cylinder stops operating. Thus, the engine is operated with the driving of only the remaining two valve-moving apparatus.
In the above-described valve-moving apparatus for an engine, the rock pin 210 is in a non-engagement condition with the low-speed rocker arm 206 in high-speed operation. However, to match timing when changed over to low-speed operation, the low-speed rocker arm 206 is urged by the low-speed arm spring 214 to always follow rotation of the cam shaft 203 and the arm parts 205 (rocker shaft parts 204). On the other hand, the rock pin 211 is in a non-engagement condition with the high-speed rocker arm 207 in low-speed operation, however, to match timing when changed over to high-speed operation, the high-speed rocker arm 207 is urged by the high-speed arm spring 215 to always follow rotation of the cam shaft 203 and the arm parts 205 (rocker shaft parts 204).
In such individual arm springs 214 and 215, since the high-speed cam 202 is large in lift amounts of the intake valve 301 and the exhaust valve 302, an acceleration acting as an inertial force is small, and the biasing force of the high-speed arm spring 215 may be relatively small. On the other hand, since the low-speed cam 201 is small in lift amount, the low-speed arm spring 214 is required to have a relatively large biasing force. Therefore, different low-speed and high-speed arm springs 214 and 215 have been used according to individual specifications.
However, when the low-speed and high-speed arm springs 214 and 215 with different specifications are used, the low-speed compression spring and the high-speed compression spring may sometimes be mistakenly assembled. If they are mistaken despite the low-speed and high-speed arm springs 214 and 215 being set for different biasing forces, the low-speed arm spring 214 tends to have an insufficient biasing force, and the high-speed arm spring 215 tends to have an excessive biasing force, which may lead to mis-operation.
With a view to eliminating such problems, it is a primary object of the present invention to provide a valve-moving apparatus for an internal combustion engine which is improved for mounting workability.